(a) Field of the Invention
The present invention relates to a method of dispersing inorganic additives uniformly in macromolecular materials.
(B) Description of the Prior Art
The art of uniformly dispersing fillers like calcium carbonate, pigments and other inorganic additives in macromolecular materials has not yet been developed sufficiently, so that, as the practical means of performing said dispersion, the use of mixers, mixing rolls and the like has been the main procedure. Meanwhile, due to the shortage of materials which has started from the petroleum crisis and the demand for materials which do not cause public nuisances or which are poorly flammable, a marked tendency to add a large quantity of inorganic filler to macromolecular materials is seen lately. In the case of paints, there is occuring a shift from the organic solvent type paint to the powder type paint by taking into consideration the environment sanitation, public nuisance, and so forth. As the method of manufacturing such powder-type paints, it is being gradually changed from the conventional roll system to the extrusion system employing an extruder from the view point of mass production, stabilization of quality, environment sanitation, economy of energy and so on. In the extrusion system, the effect of dispersing inorganic additives varies with the type of extruder, but the cause of such difference is yet to be clarified. Under the existing circumstances as set forth above, therefore, at the production plant, efforts are being exerted to improve the dispersion efficiency by analyzing each phenomenon observed and modifying the shape of screw, the condition of temperature for the cylinder, the mixing ratio of macromolecular material to inorganic additive, etc. on the basis of the result of said analysis.
When the dispersion of the inorganic additive in the macromolecular material is insufficient, it is infeasible to obtain a product with the intended properties, and the surface of the product becomes poor in glossiness and rough. Concerning powder-type paints when the dispersion of the pigment therein is insufficient, the surface of the coating film after application is dotted with fine protuberances of scores of microns in size, so that the product is unmarketable. Accordingly, when it is intended to effect uniform dispersion of inorganic additives by the use of an extruder, inasmuch as any definite prerequisite for ensuring the improvement in the quality and stability of the product has not been clarified or a thorough analysis has not been made about the dispersion mechanism of inorganic additives, the conventional extruders leave something to be desired with respect to the construction and the condition of operation.